1. Field of the Invention
This invention most generally relates to anesthesia needles used to administer regional anesthesia to a patient. More particularly the invention relates to a regional anesthesia needle used to apply anesthesia to the epidural space of a patient. Most particularly the invention relates to an epidural anesthesia needle having a slot running the length of the needle from the distal end through a hub at the proximal end. The slot allows the use of a catheter with a permanently pre-affixed connector at its proximal end for administration of anesthesia to a patient. The slot is formed with a dimension that is smaller than the outer diameter of a stylet and catheter. The smaller diameter prevents the stylet and catheter from inadvertently coming out of the needle during the procedure. Once the catheter is in place in the epidural space of a patient and secured, the needle is withdrawn and can be removed by pulling the flexible catheter out of the slot in the needle, thus allowing the use of a catheter with a permanently pre-affixed connector at its proximal end.
2. Description of the Prior Art
Regional anesthesia is performed to bring about anesthesia in a specific region of the body. The patient remains conscious of his surroundings and may retain complete mobility of the area anesthetized. When successfully performed, regional anesthesia provides complete analgesia in the specific area to which it was directed and requires only a small amount of local anesthetic. The regional anesthesia relevant to the present invention relates specifically to spinal anesthesia delivered to the epidural space, as related to the cervical, thoracic, lumbar, or caudal regions of the spine, but more specifically to the regional anesthesia performed in the lumbar or thoracic regions.
There are many preparative steps before administration of the anesthesia. The general technique of administering epidural anesthesia involves injecting a local anesthetic solution into the epidural space, from which it defuses to the immediate vertebral spaces around the injection site and around the outer layers of the spinal cord, surrounding spinal nerves, producing anesthesia. The technique is most commonly performed at the lumbar level of the spine and is applicable in the diagnosis and treatment of chronic pain, for example in cancer patients, as well as providing surgical and obstetric anesthesia.
The epidural space extends from the base of the skull to the tip of the caudal vertebrae, and lies between the dura which surrounds the spinal cord and the ligaments which join the vertebrae. The epidural space is not considered a true space, because unless separated, it is practically invisible.
Before administering the anesthesia to the epidural space, the space must first be located, and care taken not to penetrate to the spinal cord. There are two different techniques which can be used to determine when the tip of the needle has entered the epidural space; the "hanging drop", and "loss of resistance" techniques. An epidural needle is first inserted until a marked resistance is felt, indicating entry into the interspinous ligament, and up to but not through, the ligamentum flavum. At this point, in the "loss of resistance" technique, the epidural needle is advanced into the ligamentum flavum, and the stylet is removed. A syringe with an easily moving plunger is filled with air or normal saline and attached to the needle. When the needle tip is in the ligamentum flavum, air or saline can not be ejected from the syringe when pressure is applied to the plunger. Constant pressure is exerted on the plunger by one hand as the needle is slowly advanced. When the tip of the needle enters the epidural space, there is a sudden release of air or saline into the epidural space, thus the loss of resistance. Once the epidural space is located, the syringe is removed and a catheter is placed onto the needle hub, and then inserted through the epidural needle, between about 2 cm to about 4 cm past the end of the needle, into the epidural space. When the catheter is in place, the needle is then withdrawn over the catheter taking care not to move the catheter. Once the catheter is advanced past the tip of the needle the catheter cannot be withdrawn because it might be sheared by the sharp tip of the needle. If readjustment is needed, both needle and catheter must be removed together. An epidural catheter connector is then attached to the catheter to allow syringe attachment for administration of anesthesia through the catheter. The catheter is then taped in place on the patient's back.
With the above procedure in which the needle is removed by being slid over the catheter, the catheter can not have a connector "built in" or preaffixed to its proximal end because the needle would not fit over the connector. The typical connector is placed on the catheter after the needle is removed. The connector is comprised of three parts, two that are threaded together sandwiching the third part, an elastomeric tube. The catheter is slid into the connector going through the elastomeric tube. When the two threaded parts are tightened together the elastomeric tube is compressed, so its inside diameter (ID) squeezes the catheter outside diameter (OD). The problems with attaching a connector to the catheter at the time of treatment are that the connector can be over-tightened, crushing the catheter or it can be under-tightened creating a leak path or leading to the connector falling off the catheter potentially exposing the patient to extrinsic contamination. The procedure is cumbersome and the person performing the treatment may drop the connector during installation. A solution would be to have a catheter with a connector permanently or preaffixed to its proximal end by the manufacturer or at least prior to insertion of the catheter into the needle. However, the typical needle cannot be removed over a permanently or preaffixed connector.
One solution was advanced by Mohiuddin in U.S. Pat. Nos. 5,322,512 (the '512 patent) and 5,425,717 (the '717 patent). Mohiuddin's solution was to have a needle which was splittable and could break away from the catheter. The needle is removed from the catheter by breaking the needle in half along its length. Both the '512 and the '717 patents address this issue. The '512 patent deals with protecting the splittable needle, and the second includes with the splittable needle a catheter with a fixed connector. This needle can be used with a catheter having a permanently affixed connector, but presents its own problems. These problems include; the needle not splitting all the way, preventing its removal from the catheter as intended, and the needle splitting prematurely while still in the patient during placement, preventing catheter placement until the split needle is removed and another needle placed. The present invention solves the problems of the prior art by providing an epidural anesthesia needle which may be more efficiently and safely used with a catheter having a permanently affixed connector.